what caused the alteration between the barman and the old man?

Answers
1

In the pub, the old man keeps asking the bartender for a "pint," and the frustrated bartender keeps explaining to him that there are only liters and half-liters for sale. He does not know what a "pint" is. Winston buys the man a drink and begins to ask him pointed questions about the past and how things have changed since the Revolution.